The present invention concerns an electromagnetically operated jacquard steering arrangement wherein each steerable element has a magnetic system comprising a magnetic core, an anchor and a permanent magnet in which a repulsion winding is placed around the core. Each element is further provided with a coupling arm.
In a known arrangement of this type (DE-AS No. 2235225) permanent magnets are made part of the magnetic core which carries the repulsion winding. A plurality of anchors are moved towards their corresponding magnets and subsequently are returned to their starting position.
If, during this cycle the repulsion winding is not activated, the anchor is held by the magnet core. If, by operation of the repulsion winding, on the other hand, the magnetic field of the permanent magnet is neutralized, the anchor remains in its original position. The anchors operate upon intermediary elements whose position determines whether the steerable elements are displaced by a drive arrangement during a particular cycle or not.
In this known case, because the permanent magnet is located at the magnetic core it is necessary to set the repulsion current rather exactly. If that current is too small, the anchor is attracted because of the excess strength of the permanent magnet field. On the other hand, if it was too large, the anchor was pulled towards the core because of the excess strength of the electromagnetic field.
Permanent magnets are, unfortunately, sensitive to physical impact. Such impact either substantially reduces the magnetization or else the magnetic materials such as ferite ceramic, is fragile and mechanically sensitive. If one merely moves the anchor, one is then certain that in the contact phase, only the mass of the anchor and the portions connected thereto will play any part in the impact. On the other hand, if the battery of magnetic cores was moved towards the anchors, because it is impossible to control the impact time of all anchors with absolute accuracy, certain anchors will absorb a much higher impact energy than others.
There is further provided a jacquard steering arrangement in U.S. Pat. No. 4,448,046, (the disclosure of which is incorporated herein by reference) in which the retention of the anchor by the magnetic core is not caused by a permanent magnet but rather by the activation of an attraction winding which must be maintained active as long as the anchor is to be held fast to the magnetic core. In this construction, the magnetic core is fixedly located while the anchor is rotatable about an axis. The magnetic core is combined with a coupling arm which, by rotary displacement, acts positively upon a harness cord or the like. A lever arm which may be cyclically activated, presses the anchor against the magnet core.